It is generally well known that malfunctions of an engine cooling system will result in damage to the engine due to excessive engine overheating. Malfunction of an engine cooling system may result when there is a loss of coolant from the cooling system. Such a loss may occur when there is a leak in the cooling system or through a more gradual loss of coolant which may occur when operating under adverse conditions, such as driving uphill with a full load on a hot day. Alternatively, a malfunction of the cooling system may occur even without a loss of coolant. For example, if the coolant circulation system malfunctions, such as if the water pump is not working properly, the engine may overheat.
The deactivation of engine cylinders in response to engine overheating is known in the art. For example, U.S. Pat. No. 4,158,143 issued on Nov. 24, 1964 to Heidner for a "Ignition System Including Thermostatically Controlled Means For Reducing Power Output." The system disclosed in the Heidner patent includes an ignition system incorporating a thermostatic means to monitor the engine temperature. When overheating of the engine is detected, as the result of a cooling system failure for example, the thermostatic means provides a warning signal to the ignition system to interrupt the firing of at least one of the spark plugs while permitting continued sparking of at least another one of the spark plugs. Accordingly, the engine will still continue to operate, but at a reduced power level. As a result, a lesser amount of heat will be generated and the operating temperature of the engine may be reduced, thereby allowing continued operation of the engine at that reduced power level.
Regarding an electronic fuel injected engine having a pair of cylinders groups, it is also known in the art that alternately deactivating the fuel supply to those two cylinders groups will result in a cooling effect. For example, U.S. Pat. No. 4,129,109 issued on Dec. 12, 1978 to Matsumoto. In the Matsumoto patent, it is noted that the deactivation of engine cylinders can be effected by electrically cutting off the supply of injection pulses to one of the groups of engine cylinders. The resultant cooling effect is noted as follows: "Therefore, air flow is sucked into the deactivated cylinders in each cylinder cycle as well as into the activated cylinders so that the deactivated cylinder is severely cooled as compared to the activated cylinders." Matsumoto patent, column 1, lines 30-33.
As suggested by the Heidner and Matsumoto patents, the technologies disclosed in the Heidner and Matsumoto patents were combined in U.S. Pat. No. 4,473,045 issued on Sep. 25, 1984 to Bolander et al. for a "Method And Apparatus For Controlling Fuel To An Engine During Coolant Failure." The Bolander patent discloses a fuel injected engine having two groups of electromagnetic fuel injectors for first and second predetermined groups of cylinders. Fuel injection pulses are supplied to each of the fuel injector groups via one of two driver circuits. The cooling system is monitored via a conventional liquid sensing element in the coolant system and a conventional temperature sensing element mounted in the engine block. In the event the monitors detect a cooling system failure, an engine control module, described as a digital computer, deactivates the fuel injection pulses to one of the driver circuits, thereby deactivating the first of two groups of cylinders which will then be cooled by the induction of air only. After a predetermined time period substantially greater than the period of the engine cycle, the engine control module will then alternate and inhibit the supply of fuel to the second of the two groups of cylinders while allowing fuel to be supplied to the first group of cylinders.
The apparatuses and methods disclosed in these prior art patents leave a number of problems unsolved. First, deactivation of cylinders based upon coolant level or engine block temperature may not be sufficient to prevent damage. In the event of a circulation malfunction within the cooling system, a liquid sensor may not detect any problem at all and an engine block temperature sensor may not detect a problem until damage occurs to the cylinder head.
Second, instead of relying on the deactivation of a set predetermined group of cylinders, it may be desirable to deactivate a variable number of cylinders depending on the load conditions. In other words, it may be desirable to deactivate one or more of the cylinders, up to one less the total number of cylinders. For example, under low load conditions, it may not be necessary to deactivate more than one or a small number of cylinders. Likewise, under heavy load conditions, it may be desirable to deactivate a larger number of cylinders, up to one less than the total number of cylinders.